Restricted space and the ever increasing degree of circuit integration have set demands in the manufacturing of electronics in many ways, in various fields of component making. Surface mounted components have been decreasing in their size, thus facilitating large amounts of them to be integrated on to a printed wiring board. Similar physical size decreasing trend has been also going on in the field of microelectromechanical systems (MEMS). The evolution of the design has led to integration in very high level and finally to stacked structures, when the demand of mounting space has increased even faster than the component size decrease as such.
A patent publication EP1951609 describes a system-in-package device where a MEMS-die and an integrated circuit (IC) die are stacked on top of each other. FIG. 1 illustrates a system-in-package device applying this known configuration where external electrical contacts are provided on the surface of the bigger of the two dies. This kind of system-in-package device is applicable when one of the dies is significantly smaller than the other die, thus leaving room for contact areas on the surface of the bigger die. To be practically applicable, the smaller die has also to be quite thin, below 0.2 mm.
Another example of prior art is given in patent publication U.S. Pat. No. 6,405,592B1. Also there only certain size ratios of the two dies are allowed.
For commercially feasible applications, dies to be included in system-in-package devices come from various sources and their dimensions are already predetermined at the time of their use for system-in-package device production. As long as the system-in-package device configuration is simple and the dies to be packaged appropriately match in size such that any necessary components or wiring, like external electrical connections, can be provided on the larger die, the solution of EP1951609 is applicable. However, when the dies are quite close in size, the conventional method cannot be used since there is no room for other necessary elements, like contacting members that provide necessary input/output functions of the system-in-package device. Due to this mismatch problem, many functionally advantageous and desired system-in-package configurations have not yet become commercially available.